This present invention relates to the field of microprocessors, and in particular to a networked processor having a network co-processor, for use in a motor vehicle.
In automobiles, microprocessors (hereinafter generally referred to as “processors”) in combination with various transducers and sensors, are performing a wide variety of control, monitoring and indicating functions. The processors, transducers, and sensors, which are relatively far apart from each other in the vehicle, typically exchange data or signals via standardized automotive networks whose active data interfaces handle the data traffic via standardized protocols and bus lines. The processors control the data exchange (i.e., the network management tasks) via suitable additional executable programs or suitable additional circuits. The areas of the processor that execute the network management tasks with this additional software and hardware can be referred to as a “network processor”.
Known motor vehicle network standards include: the Controller Area Network (CAN), K-Line Interface, Vehicle Area Network (VAN), J1850, SPI Net, and TTP. Each of these networks generally employs a two-wire bus over which packetized data is transferred according to the respective standardized data format and protocol. For example, in the CAN network, each packet contains up to eight 8-bit words and the data transfer is serial. The data transfer rate is adapted to the field of tasks of the data to be transferred, and ranges for example from 125 to 500 kbs. For example air conditioning control may be assigned a low bit rate and low priority, while braking and anti-slip control for the individual wheels may be assigned a high bit rate and high priority.
If more than two nodes are connected to a network processor, a priority controller is necessary to control contention in the event of simultaneous access to the data bus. In addition, measures have to be taken that permit the transfer of larger amounts of data by partitioning the data into packets at the sending end, and sending the packets separately. At the receiving end the packets are reassembled in the correct order to reconstruct the message for further processing.
These control functions are performed under the control of executable software within the respective processor (e.g., generally in the associated RAM/ROM memories). The software has a three-layer structure, with the individual layers corresponding to a hierarchically organized functional sequence of the data transfer. A detailed description of such a network or transmission standard can be found, for example, in a document provided by the OSEK Group (i.e., in German, Offene Systeme und deren Schnittstellen für die Elektronik im Kraftfahrzeug, and in English, Open Systems and the Corresponding Interfaces for Automotive Electronics), entitled “OSEK Communication Specification”, Version 1.00, Sep. 11, 1995, COM Specification 1.00. For the further considerations, however, a brief outline of these three layers will be sufficient.
The lowest of the three layers is the Data Link Layer (DLL), which is concerned with the transfer of the packet data format and determines the associated data format and the degree of error correction. This layer also controls priority in the event of a collision, handles the communications protocol, and controls the hardware required as network drivers in the respective nodes.
The overlying layer is the Transport Layer (TL), which permits the exchange of data that cannot be accommodated in a single packet due to its length. At the sending end, a transport protocol is created so that at the receiving end, the individual transmitted segments can first be stored and then be reassembled in proper sequence. The number of associated segments and other important information, such as the type of content, are also recorded in the transport protocol and transferred. The counterpart of exceptionally long information is short information, for instance the transfer of a single bit. To prevent the network from being blocked for the entire duration of the transmission of a packet with a size of, for example 8×8 bits, including the header information, a short message can be activated by transport layer.
Support of the Higher-Layer function is possible by a Transport Layer coprocessor that relieves the processor of the task of translating the messages of the Transport Layer into the respective node messages (i.e., into the associated DLL message). At the same time, the interrupt load on the processor proper is reduced, since the interrupts are initiated not after each transfer of a node message, but only after transfer of a Transport Layer message. An example of such support is described in the publication “Proceedings ICC '99, 6th International CAN Conference”, Turin, 2 to 4 November, page 09-27 to page 09-33, in an article entitled “New Generation of CAN Controller Supporting Higher Layer Protocols”. 
A problem with these conventional vehicle networks is the load placed on the processor to support the transmission of data over the network. Therefore, there is a need for a vehicle network system that reduces the processing load associated with the network tasks on the main processor.